[Windows 8] How to launch an app using NFC tags?

Here is a quick (but quite useful) tip for anyone who want to use NFC tags on its application.

NFC tags can be used on Windows (Phone) to open Internet links but they can also be used to open a particular application on your system.

For that, you just need to use/create a LaunchApp message that will be written on the tag:

var proximityDevice = Windows.Networking.Proximity.ProximityDevice.getDefault();
if (proximityDevice) {
    proximityDevice.ondevicearrived = function(device) {
        var launchArgs = "user=Thomas LEBRUN";

        // Package.manifest -> View XML Source -> <Application Id="...">
        var appId = "App";

        var appName = Windows.ApplicationModel.Package.current.id.familyName + "!" + appId;

        var launchAppArgs = launchArgs + "\tWindows\t" + appName;

        var dataWriter = new Windows.Storage.Streams.DataWriter();
        dataWriter.unicodeEncoding = Windows.Storage.Streams.UnicodeEncoding.utf16LE;
        dataWriter.writeString(launchAppArgs);

        var launchAppId = proximityDevice.publishBinaryMessage("LaunchApp:WriteTag", dataWriter.detachBuffer());
       proximityDevice.stopPublishingMessage(launchAppId);
   };
}

The content of the tag is a string, where all the items are separated by “\t”:

1. Some arguments that you want to use when the app starts
2. The plateform (in our case, we need to specify “Windows”)
3. The application name, which contains:
1. The application id (this one can be found in the manifest file, under the attribute Id of the tag Application)
2. The current package family name

Using this parameters, we can publish a particular message: LaunchApp:WriteTag. This tag/message will be recognize by the platform which will then ask for the user to open the dedicated application.

So you can easily imagine use this technique to create an new kind of authentification in your application (at least to provide the username).

Happy coding!